For large transfers eg. image previews, particularly with SSL's
protocol limit of 16k byte blocks, we see lots of inefficiency
repeatedly copying a 20Mb image and shuffling it down a
std::vector as we write data out.
Change-Id: I620568cad2e6f41684c35289b0ee77cf7f59c077
Signed-off-by: Michael Meeks <michael.meeks@collabora.com>
